Neighbor iterator v0.3

local function neighborInSequence(reference, lastNeighbor)
    local newNeighbor, costToNeighbor
    local dX, dY
    if not lastNeighbor then
        dX, dY = -1, 0
    else
        dX, dY = lastNeighbor.xTile - reference.xTile, lastNeighbor.yTile - reference.yTile
    end
    dX, dY = -dY, dX
    if dY = -1 and lastNeighbor then
        return
    end
    newNeighbor = reference.parent[reference.yTile + dY][reference.xTile + dX]
    if newNeighbor.isTraversable then
        costToNeighbor = 1
    else
        costToNeighbor = math.huge
    end
    return newNeighbor, costToNeighbor
end